2013 Chemistry Higher (Revised) Finalised Marking … MARKING ADVICE: Chemistry Higher (Revised) The...

2013 Chemistry

Higher (Revised)

Finalised Marking Instructions

Scottish Qualifications Authority 2013

The information in this publication may be reproduced to support SQA qualifications only on a non-commercial basis. If it is to be used for any other purposes written permission must be obtained from SQA’s NQ Assessment team. Where the publication includes materials from sources other than SQA (secondary copyright), this material should only be reproduced for the purposes of examination or assessment. If it needs to be reproduced for any other purpose it is the centre’s responsibility to obtain the necessary copyright clearance. SQA’s NQ Assessment team may be able to direct you to the secondary sources. These Marking Instructions have been prepared by Examination Teams for use by SQA Appointed Markers when marking External Course Assessments. This publication must not be reproduced for commercial or trade purposes.

©

Part One: General Marking Principles for Chemistry Higher (Revised) This information is provided to help you understand the general principles you must apply when marking candidate responses to questions in this Paper. These principles must be read in conjunction with the specific Marking Instructions for each question.

(a) Marks for each candidate response must always be assigned in line with these general marking principles and the specific Marking Instructions for the relevant question.

(b) Marking should always be positive ie, marks should be awarded for what is correct

and not deducted for errors or omissions.

GENERAL MARKING ADVICE: Chemistry Higher (Revised)

The marking schemes are written to assist in determining the “minimal acceptable answer” rather than listing every possible correct and incorrect answer. The following notes are offered to support Markers in making judgements on candidates’ evidence, and apply to marking both end of unit assessments and course assessments. General information for markers

The general comments given below should be considered during all marking.

1. There are no half marks awarded.

2. Marks should not be deducted for incorrect spelling or loose language as long as the meaning of the word(s) is conveyed.

Example: Answers like 'distilling' (for 'distillation') and 'it gets hotter' (for 'the temperature rises') should be accepted.

3. A right answer followed by a wrong answer should be treated as a cancelling error and no marks should be given.

Example: What colour is seen when blue Fehling’s solution is warmed with an aldehyde?

The answer 'red, green' gains no marks.

4. If a right answer is followed by additional information which does not conflict, the additional information should be ignored, whether correct or not.

Example: Why can the tube not be made of copper?

If the correct answer is related to a low melting point, 'Copper has a low melting point and is coloured grey' would not be treated as having a cancelling error.

5. Full marks are usually awarded for the correct answer to a calculation on its own; the part marks shown in the marking scheme are for use when working is given. An exception is when candidates are asked to 'Find, by calculation, '.

6. A mark should be deducted for incorrect or missing units only when stated in the marking scheme. No marks should be deducted for incorrect or missing units at intermediate stages in a calculation.

7. As a general rule, where a wrong numerical answer (already penalised) is carried forward to another step, no further penalty is incurred provided the result is used correctly. The exception to this rule is where the marking instructions for a numerical question assign separate “concept marks” and an “arithmetic mark”. In such situations, the marking instructions will give clear guidance on the assignment of partial marks.

8. Ignore the omission of one H atom from a full structural formula provided the bond is shown.

9. A symbol or correct formula should be accepted in place of a name unless stated otherwise in the marking scheme.

10. When formulae of ionic compounds are given as answers it will only be necessary to show ion charges if these have been specifically asked for. However, if ion charges are shown, they must be correct. If incorrect charges are shown, no marks should be awarded.

11. If an answer comes directly from the text of the question, no marks should be given.

Example: A student found that 0 · 05 mol of propane, C3H8 burned to give 82 · 4 kJ of energy.

C3H8(g) + 502(g) 3CO2(g) + 4H2O(ℓ)

Name the kind of enthalpy change which the student measured.

No marks should be given for 'burning' since the word 'burned' appears in the text.

12. A guiding principle in marking is to give credit for correct chemistry rather than to look for reasons not to give marks.

Example 1: The structure of a hydrocarbon found in petrol is shown below.

Name the hydrocarbon.

Although the punctuation is not correct, '3, methyl-hexane' should gain the full mark.

Example 2: A student measured the pH of four carboxylic acids to find out how their strength is related to the number of chlorine atoms in the molecule.

The results are shown.

How is the strength of the acids related to the number of chlorine atoms in the molecule?

Although not completely correct, an answer such as 'the more Cl2, the stronger the acid' should gain the full mark.

13. Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemistry, a non-chemical answer gains no marks.

Example: Why does the (catalytic) converter have a honeycomb structure?

A response such as 'to make it work' may be correct but it is not a chemical answer and the mark should not be given.

CH3 CH2 CH CH2 CH2 CH3

CH3

Part Two: Marking Instructions for each Question Section A

Question Acceptable Answer Question Acceptable Answer

1 B 16 C

2 D 17 B

3 C 18 C

4 C 19 B

5 D 20 A

6 D 21 A

7 A 22 D

8 C 23 C

9 D 24 B

10 B 25 A

11 A 26 B

12 C 27 A

13 D 28 A

14 C 29 B

15 A 30 D

Question Acceptable Answer/s Max Mark

Unacceptable

1 a i K(g) → K+(g) + e– (1)

K(g) → K+(g) + e (1)

1 Missing or incorrect state symbols

1 a ii Answers can be given either in terms of

potassium or of chlorine Answers starting with “it” are assumed to refer to Potassium Either K has more shells/levels or electron further from nucleus or diagram showing this (1) Correct and clear use of greater shielding/screening (or clear explanation thereof) (1) So less energy required to remove electron/ weaker attraction for the electron (1)

3

or Cl has fewer shells or electron closer to nucleus (1) Correct and clear use of less shielding/screening (or clear explanation thereof) (1) So more energy required to remove electron/stronger attraction for the electron (1)

1 b 8 1 Circling OH groups but not

stating the number

Question Acceptable Answer/s Max

Mark Unacceptable

2 a It can react with radicals to form stable

molecules (1) or It can terminate radical (reactions) (1) or It reacts with radicals to stop further radical reactions (1) or It mops-up (free) radicals (1) or It has an unpaired/free electron (1)

1 Provides electrons (0)

2 b C6H8O6 C6H6O6+ 2H+ + 2e–

(state symbols not required, negative sign on electron not required)

1


Mark Unacceptable

3 a Stating that one (CHCl3) is polar and/or the

other (CCl4) is non-polar (1) Identifying that CHCl3 has permanent dipole/permanent dipole attractions and identifying that CCl4 has London dispersion forces (1) Other mark is for a statement linking intermolecular forces/polarity to the solubility in water. Statements such as the following would be acceptable

Water is polar (1)

Water has permanent dipole/ permanent dipole attractions (1)

Water is a good solvent for polar molecules (1)

Like dissolves like (1)

3

3 b -97 (2) 2 A single mark is available if either of the

following operations is correctly executed

Either the four relevant values for the bond enthalpies

of the C–H, Cl–Cl, C–Cl and H–Cl bonds (or multiples thereof) are retrieved from the databook; 243, 414, 326, 428 (ignore signs) (1)

or the enthalpy values for bond formation are taken

away from the enthalpy values for bond breaking without arithmetic error (1) (units not required)


Unacceptable

4 a i Tollen’s or acidified dichromate or Fehling’s or

Benedict’s (please note – although Benedict’s reagent would not work in practice, because it appears in Higher textbooks, revision guides and the PPA materials for the traditional Higher, it can be accepted) (accept other spellings if phonetically correct)

1

4 a ii Carboxylic acid 1

4 b i It keeps oil & water soluble materials mixed

or Allow immiscible substances to mix or To allow fat and water to mix or To form a suspension

1 to stop it separating (with no mention of water & oil soluble components) to stop layers forming

4 b ii H H H

H C C C H OH OH OH

1

Any structural formula for glycerol

4 c 6·7 (mg) – units not required

A single mark is available if either of the following manipulations is correctly executed.

2

Correct use of percentage

eg mass of chocolate = 28

× 17 g = 4·76 g

100 Correct use of proportion theobromine eg mass of theobromine = 1·4 × a mass


Mark Unacceptable

4 d This is an open ended question

1 mark: The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 marks: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 marks: The maximum available mark would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically correct answer to the question posed. This type of response might include a statement of the principles involved, a relationship or an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an ‘excellent’ answer or a ‘complete’ one.

3 The student has demonstrated no understanding of the chemistry involved. There is no evidence that the student has recognised the area of chemistry involved or has given any statement of a relevant chemistry principle. This mark would also be given when the student merely restates the chemistry given in the question.


Unacceptable

5 a 75 % (2)

2

Total mass of reactants/products = 240 g (1)

Atom Economy = 180

× 100 % = 75 % (1)

240 (Accept 0·75 also, this would be atom

economy as a fraction)

5 b 40 % (2) 2

1 mark is given for either calculating the theoretical yield, or for working out the numbers of moles of reactant and product formed. eg 6•55(g) or both 0•0364 and 0•0146 1 mark is given for calculating the % yield; either using the actual and theoretical masses, or using the actual number of moles of products and actual number of moles of reactant.

%yield = 2·62

× 100 5·02 = 52·2 %


Mark Unacceptable

6 a i Carboxyl (group) (1)

or Carboxylic (acid) (1)

1

6 a ii CH3

CH3

N

H

H

1

6 a iii

C

O

CH2 N

CH2

CH2 CH3

CH3

O-

Na+

1 Covalent bond shown between Na-O

or shortened formula. Charges not required but if shown, both +ve and –ve charges must be correct(1).

6 b 25 (minutes)

or 8.0 to 8.4 (minutes) (units not required. Ignore incorrect units)

1


Mark Unacceptable

6 c Volume = 31·5 cm3 or 31·5 ml or 0·0315 l or

equivalent (3) One mark is allocated to the correct statement of units of volume. This is the mark in the paper earmarked to reward a candidate’s knowledge of chemical units. So volume = 31·5 or 0·0315 (2) One mark is available if either of the following steps is correct Calculation of mass of lidocaine eg 4·5 × 70 = 315 (mg) Calculation of a volume of solution required

3

eg a mass ×

1 = a volume

10

6 d i Benzocaine is a smaller/Tetracaine is

bigger (1) or weaker London Dispersion Forces with Benzocaine (1) or weaker Van der Waal’s forces for Benzocaine (1) or Benzocaine has lower b.pt (1) or Benzocaine more soluble/attracted in/ to mobile phase (1) or Benzocaine less strongly attracted to stationary phase (1) or Benzocaine is more polar (1)

1 Benzocaine takes less time to travel through the apparatus

6 d ii The peaks for lidocaine and caffeine overlap

or Candidate wording for idea of masking

1 The retention times are similar


Mark Unacceptable

Peak for tetracaine at correct RT with approximately half original height

1

6 d iii


Unacceptable

7 a i For successful generation of gas;

must have iron sulfide, hydrochloric acid and appropriate glassware to transfer the gas to the gas collection/ measurement apparatus without loss of gas (1) For the successful collection and measurement of the gas; must have a syringe or collect the gas in a measuring cylinder over a non- aqueous liquid (1)

2

7 a ii 0·29 (g) (units not required)

1 mark is awarded for a correct strategy to work out number of moles of hydrogen sulfide (a volume of hydrogen sulfide in whatever unit is shown being divided by a molar volume in whatever unit). 1 mark is awarded for correct strategy to work out the mass of the iron(II) sulfide (eg a number of moles of FeS is multiplied by something clearly intended to be the GFM of FeS). 1 mark is awarded for correct arithmetic in both of these steps. (This includes the correct value for the GFM of FeS). This arithmetic mark can only be awarded if both of the concept marks are awarded.

3

7 b i Covalent molecular

or discrete covalent

1

7

b

ii

Al2S3 + 6H2O 2Al(OH)3 + 3H2S Correct formulae for all but one substance, whether balanced or not – 1 mark

2


Mark Unacceptable

8 a –803, 726, 283

(any two values from this list) (1) +206 kJ mol–1 (for value, no follow through, units not required) (1)

2

8 b 1

temperature decrease/keep the same/increase

pressure decrease/keep the same/increase

9 a 9·0 1

9 b 4 1

10 a I2 + 2e– 2I– (1)

or I2 + 2e 2I– (1) Ignore state symbols Allowing reversible arrows providing the equation is written the correct way round.

1

10 b i first titre is a rough (or approximate)

result/practice or first titre is not accurate/not reliable/rogue or first titre is too far away from the others or you take average of concordant/close results (1)

1


Unacceptable

10 b ii 0·045 (mol l–1 – units not required)

3 marks Partial marks can be awarded using a scheme of two “concept” marks, and one “arithmetic” mark. 1 mark for knowledge of the relationship between moles, concentration and volume. This could be shown by any one of the following steps:

Calculation of moles thiosulfate(aq) eg 0·1 × 0·01815 = 0·001815

Calculation of concn I2 eg (0·000908) ÷ 0·02 = 0·045

Insertion of correct pairings of values for concn and volume in a valid titration formula such as

3

C1V1

= C2V2

eg 18·15 × 0·10

= C2 × 20·0

b1 b2 b1 b2 1 mark for knowledge of relationship

between moles of S2O32– and l2. This

could be shown by any one of the following steps:

Calculation of moles I2 from moles S2O3

2– eg 0·001815/2 = 0·000908

Insertion of correct stoichiometric values in a valid titration formula such as

C1V1

= C2V2

eg 18·15 × 0·10

= C2 × 20·0

b1 b2 2 1 1 mark is awarded for correct arithmetic

throughout the calculation. This mark can only be awarded if both concept marks have been awarded.

10 b iii Mass of sodium thiosulfate = 3·96 g (1)

Mention of rinsings (1) Mention of make up to the mark (1)

3


Mark Unacceptable

11 a i (anaerobic) fermentation

or Anaerobic respiration

1

11 a ii 10·1 to 10·3 (% abv) 1 11

11 b i 114 or 113·75 1

11 b ii £3·30

(do not penalise for rounding at intermediate stages) One mark is available if the candidate has either

2

Carried out a calculation to take into account the dilution of the whisky

e.g. used a scaling factor of

46

65

or

Has correctly calculated the cost for a given volume of alcohol by use of the

e.g. used the scaling factor of 1300/195

11 b iii 5-butyl-4-ethyltetrahydrofuran-2-ol

or 4-ethyl-5-butyltetrahydrofuran-2-ol

1

11 c i addition or hydration 1

11 c ii no change 1


Mark Unacceptable

12 This is an open ended question

1 mark: The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 marks: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 marks: The maximum available mark would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically correct answer to the question posed. This type of response might include a statement of the principles involved, a relationship or an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an ‘excellent’ answer or a ‘complete’ one.

3 The student has demonstrated no understanding of the chemistry involved. There is no evidence that the student has recognised the area of chemistry involved or has given any statement of a relevant chemistry principle. This mark would also be given when the student merely restates the chemistry given in the question.


Mark Unacceptable

13 a

1 Structures with missing H-atoms Any structure with a methyl group in the equatorial position.

or equivalent 1,3-dimethylcyclohexane structure with both methyl groups in axial positions

13 b i The bigger the group the greater the strain

or The larger the (halogen) atom the greater the strain or The more atoms in a group, the greater the strain or Any other statement which is consistent with the values presented

1 Incorrect reference to a group as a “molecule”

13 b ii 7·6 (kJ mol–1)

(Units not required, ignore incorrect units) 1

[END OF MARKING INSTRUCTIONS]

2013 Chemistry Higher (Revised) Finalised Marking … MARKING ADVICE: Chemistry Higher (Revised) The...

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